In this research, we shall investigate disturbances affecting patients' abilities to recognize auditorily presented words ("auditory lexical access"). Most view of auditory lexical access assume that the sound waveform is analyzed in such a way as to provide the listener with acoustic parameters that correspond to the phonetic features of the sounds of words. For instance, the work BAT begins with a voiced bilabial stop consonant, and each of these features is thought to be extracted from the acoustic stimulus. A word is accessed when a listener detects in the sound stimulus acoustic properties that are correlates of these features and matches this pattern of acoustic properties to features in the stored lexicon. Subsequent to this stage of accessing a word on the basis of its form (lexical access), the meaning of the word is activated (semantic access), along with other features such as syntactic information. In the proposed research, we shall systematically examine the nature of disturbances in identifying and discriminating a number of phonetic contrasts that occur in English phonemes, and relate these disturbances to impairments in lexical access. The basic approach will be to synthesize various auditory stimulus continua in which particular acoustic parameters are manipulated. Subjects will be tested for their ability to identify and discriminate between items on these continua. Subjects will then be tested for their abilities to identify and discriminate phonemes in non-words in natural speech stimuli, and on a variety of measures designed to indicate whether specific lexical items are activated normally in the auditory modality. This series of tests will identify disturbances in extracting the basic phonetic features from speech, and examine the consequences of these disturbances for recognizing auditorily presented words. We will correlated these disturbances for recognizing auditorily presented words. We will correlated these disturbances with neuro-radiological measurements of lesion size and location (MRI scanning. The results will be of use in diagnostic assessment and treatment planning for patients with language disorders, and will contribute to our understanding of the neural basis for language.